Typical water runoff contains a surprisingly large amount of oil and other contaminants. The resulting contamination of natural receiving water incurs enormous annual costs, both financial and environmental. For example, a government study in one published article showed that storm water sampled from street sites contained an xe2x80x9cevent mean concentrationxe2x80x9d of 2.2 mg. of oil per liter of runoff water. Shepp, xe2x80x9cPetroleum Hydrocarbon Concentrations Observed in Runoff from Discrete, Urbanized Automotive-Intensive Land Uses,xe2x80x9d Watershed ""96. If one meter of rain per year falls on a street 10 meters wide, then at that observed mean rate, the annual runoff from each kilometer of street will- contain about 275 liters of hydrocarbons.
To mitigate this problem, various types of filters have been developed for use in water drains. For example, U.S. Pat. No. 5,849,198 to Sharpless discloses a filter cartridge containing oil absorbing material, which is suspended below the grate of a storm drain by flexible suspension elements such as chains. The top of each of the flexible suspension elements terminates at an attachment element that engages the grate of the storm drain.
To maintain its effectiveness, a runoff filter or catchment basin requires regular maintenance. Filter modules or cartridges containing filter media must be replaced or serviced when the media becomes saturated. The Sharpless patent teaches a replacement technique in which the filter cartridge is lifted up and out of the drain""s catch basin as the grate is removed. This process requires simultaneous lifting of the weight of the grate and the filter cartridge. Typically, a filter cartridge being replaced contains accumulated trash or saturated filter media or both, and it can be very heavy. Considerable force is needed to dislodge a heavy metal rate from its catch basin and lift the grate and the filter cartridge out of the basin together.
In view of these and other problems associated with conventional runoff filters, the need remains for improved runoff filters that can be more easily maintained while still accommodating excess runoff under storm conditions. A further need remains for runoff filters that can be more efficiently manufactured, stored, and shipped and disposed of with reduced environmental consequences.
A filter system according to various aspects of the present invention includes a bracket and a filter module suspended from the bracket by a plurality of flexible supports. The bracket supports the filter system beneath the grate of a storm drain without the need for the filter system to be attached to the grate. Advantageously, the grate can be lifted out of the storm drain before and separately from the filter unit for replacement, servicing, or cleaning of the filter module. After the grate has been removed, a vacuum hose can be inserted into the filter module for removal of trash and debris. In addition, this capability allows the filter system to be lifted without the added weight of the grate. When the grate has been lifted out of the way, suitable fasteners can attach the filter unit to the bracket of the filter system to make the use of mechanical lifting devices more convenient.
The use of flexible supports allows suspension of the filter module from the bracket in more storm drain configurations than would be possible with a rigid arrangement. Flexible supports permit the filter module to deviate from hanging directly beneath the bracket, thus allowing the filter module to fit into the storm drain even when obstructions protrude into the volume directly beneath the bracket.
According to one aspect of the invention, the filter system can employ a bracket sized to be supported without the need for fasteners to either the grate or the edges of the storm drain. Such a bracket includes a flat supporting edge structure along at least a portion of its perimeter. The supporting edge structure extends outward from the bracket so that the edge structure can be supported along the edges of the storm drain and held in place by the weight of the grate. By avoiding the need for fasteners, a filter system having such a bracket can be more conveniently lifted out of the storm drain. The bracket can be manufactured to known dimensions. Advantageously, the bracket can be marketed by offering it from among a set of brackets that are pre-configured for known storm drain dimensions or as a standard bracket that can be modified to fit the dimensions of a particular storm drain.
According to another aspect of the invention, the filter system can employ a filter module that includes filter media disposed about an open recess. Such a configuration permits trash to accumulate in a region surrounded by filter media. Surprisingly, accumulated trash actually enhances performance of the filter module by improving hydrocarbon removal efficiency. In the presence of water, many types of contaminants tend to stick to the materials typically found in trash from urban runoff. By permitting trash to accumulate in a region surrounded by a filter media, the filter module advantageously employs trash as a cost-free pre-filtering media. Indeed, the trash can be removed several times over the useful life of the filter media, if desired. This advantageous filter module configuration makes maintenance easier by providing convenient access to a person inserting a vacuum hose or reaching down from above the storm drain to clean out the accumulated trash.
A filter system according to another aspect of the invention includes a tray supporting the filter module, that can couple to the bracket by flexible supports. In such a system, the filter module is configured such that its bottom can rest on the tray. By providing a tray to support the bottom of the filter module, the filter module can require less supporting structure. With less structure, the filter module has less material requiring disposal and consequently can be manufactured less expensively and reduce adverse environmental impact.
In a filter system according to another aspect of the invention, the filter module includes a sectional shell, which includes a plurality of planar sections. The sections are joined together such that each section is bendably joined to an adjacent section. In a first (stored) configuration, the sections lie substantially in the same plane. In a second (assembled) configuration, the sections do not all lie substantially in the same plane and the sections substantially enclose the filter media. Advantageously, the sectional shell can assemble entirely from planar sections, simplifying manufacturing and permitting flat storage of the shell""s components before assembly. By bonding the planar sections together using ultrasonic welding, according to a particular aspect of the invention, fasteners such as rivets or staples can be avoided, which further simplifies manufacturing. In addition, the need for disposing of multiple types of material, and consequent adverse environmental impact, is reduced. The planar sections can be fabricated from a single piece of sheet material, still further simplifying manufacturing.
According to another aspect of the invention, filter media can have the form of a coherent block of agglomerated fragments. Advantageously, a filter module including media in that form requires less structure to support the media.
According to another aspect of the invention, the bracket can be advantageously configured to act as a funnel. By directing water downward to the filter module, a bracket having such a configuration helps maximize the amount of water that passes through the filter module.
According to a method of the invention, purity of water entering a storm drain having a grate can be improved by installing and replacing filter modules in the storm drain. A first filter module suspends from at least two edges of the storm drain below the grate. To replace the first filter module with a second filter module (of the same or a different type), the grate is removed from the storm drain while the first filter module remains suspended from the edges of the storm drain. The first filter module is then lifted out of the storm drain and replaced with the second filter module. Other aspects of the invention reside in tools useful for such lifting.
The above summary does not contain an exhaustive list of all aspects of the present invention. Indeed, the inventors contemplate that their invention includes all systems and methods that can be practiced from all suitable combinations of the various aspects summarized above, as :well as those disclosed in the detailed description below and particularly pointed out in the claims filed with the application. Such combinations have particular advantages that may or may not be specifically recited in the above summary.